Electromagnetic torque measuring instrumentation for a rotating shaft

Abstract

A method and apparatus for continuously monitoring torque in a rotating shaft. The invention includes a pair of electromagnetic probes in fixed proximity to the shaft and spaced-apart in the direction of the shaft's longitudinal axis. The probes are operable in two modes. In the first, each probe is excited to cause a fixed magnetic pattern to be induced onto the surface of the shaft along a circumferential line adjacent to the probe. In the second mode, movement of the magnetic pattern due to the shaft rotation induces a signal into each probe. Each signal is indicative of the instantaneous angular velocity of the shaft at the corresponding shaft location. The two induced signals are conveyed to phase detection circuitry which produces a signal indicative of the phase relationship between the two input signals. The electrical phase relationship is a direct measure of the twist in the shaft, proportional to torque.

The invention claimed is: 
     
       1. Torque monitoring instrumentation for continuously measuring torque between first and second axially separate locations on a rotating shaft, comprising: first and second electromagnetic probes fixed with respect to said shaft and located in proximity to the surface thereof at said first and second locations, respectively, said first and second probes being operable in a first mode to induce a fixed circumferential magnetic pattern on to the surface of said shaft at said first and second locations, respectively, and being operable in a second mode to produce first and second output signals, respectively, in response to the movement of said magnetic patterns as said shaft is rotating, said first and second output signals each having a frequency indicative of the instantaneous angular velocity of said shaft at said first and second locations, respectively;   switching means operable to switch said first and second probes between said first and second modes;   excitation means for generating an excitation signal and for supplying said signal to said first and second probes in said first mode to cause said probes to induce said fixed circumferential magnetic patterns, said excitation means including means for synchronizing the frequency of said excitation signal with shaft speed so that said fixed circumferential magnetic pattern is invariant with shaft speed in said first mode; and   phase detection means operable in combination with said first and second probes in said second mode to receive said first and second output signals and to produce a phase signal indicative of the phase relationship between said first and second output signals, said phase relationship being indicative of the torque on said shaft between said first and second locations.   
     
     
       2. The invention of claim 1 further including: first capacitor means connected to said first and second probes in said first mode to form first and second series resonant circuits; and   second capacitor means connected to said first and second probes in said second mode to form first and second parallel resonant circuits.   
     
     
       3. The instrumentation of claim 2 wherein said excitation means includes means for slowly increasing the peak-to-peak amplitude of said excitation signal. 
     
     
       4. The instrumentation of claim 3 wherein said excitation means includes a phase locked loop and a freqency divider for generating said excitation signal, and said means for synchronizing said excitation signal includes a shaft speed sensor providing a synchronizing signal to said phase locked loop. 
     
     
       5. The instrumentation of claim 4 wherein said phase detection means comprises: pulse shaping circuitry responsive to said first and second output signals to produce first and second pulse signals; and   a flip-flop responsive to said first and second pulse signals to produce said phase signal as a function of time duration of pulses produced by said flip-flop.   
     
     
       6. The instrumentation of claim 5 wherein said phase detection means further includes a low pass filter connected to receive said pulses from said flip-flop. 
     
     
       7. The instrumentation of claim 6 wherein said means for slowly increasing the peak-to-peak amplitude of said excitation signal comprises an analog multiplier providing the excitation signal as the product of a slowly increasing voltage and a signal output from said phase locked loop. 
     
     
       8. The instrumentation of claim 7 wherein said excitation means includes a power amplifier for amplifying said excitation signal. 
     
     
       9. For use in continuously measuring the torque between axially separate locations on the central rotating shaft of a turbine-generator set, apparatus comprising: a first electromagnetic probe in fixed proximity to the surface of said shaft at a first one of said axial locations and a second electromagnetic probe in fixed proximity to the surface of said shaft at a second one of said axial locations, said first and second probes each being adapted for operation in a first mode to induce a fixed circumferential magnetic pattern onto the surface of said shaft at their respective locations and for operation in a second mode to produce corresponding first and second output signals in response to the motion of said magnetic pattern during shaft rotation;   excitation means supplying an excitation signal to said first and second probes during said first mode to cause said probes to induce said magnetic patterns, said excitation signal having a frequency which is proportional to the rotational speed of said shaft;   first capacitor means disposed in said first mode to form first and second series resonant circuits with said first and second electromagnetic probes, respectively, each series resonant circuit being resonant at the frequency of said excitation signal;   second capacitor means disposed in said second mode to form first and second parallel resonant circuits with said first and second electromagnetic probes, respectively, each parallel resonant circuit being resonant at the frequency of said excitation signal;   phase detection means adapted to receive said first and second output signals and to provide a phase indicative signal proportional to the phase separation between said first and second output signals, said phase indicative signal being characteristic of the torque between said first and second locations; and   means for selectively switching between said first and second modes.   
     
     
       10. The apparatus of claim 9 wherein said excitation means includes a phase locked loop and a frequency divider for generating said excitation signal in response to a signal provided by a shaft speed sensor. 
     
     
       11. The apparatus of claim 10 wherein said excitation means further includes means for slowly increasing the peak-to-peak amplitude of said excitation signal. 
     
     
       12. The apparatus of claims 9, 10, or 11 wherein said phase detection means comprises pulse shaping circuitry for producing pulses indicative of the phase relationship between said first and second output signals, and a flip-flop for producing said phase indicative signal in response to the phase separation between such pulses. 
     
     
       13. The apparatus of claim 12 wherein said means for selectively switching between said first and second modes is a manually operated switch. 
     
     
       14. A method for measuring the torque between axially separate locations on a rotating shaft, comprising the steps of: (a) inducing a first fixed circumferential magnetic pattern onto the surface of the shaft during shaft rotation at a first location thereon independent of shaft speed;   (b) inducing a second fixed circumferential magnetic pattern onto the surface of the shaft during shaft rotation at a second location thereon independent of shaft speed, said second location being axially spaced apart from said first location;   (c) generating a first signal in a first sensing probe responsive to the movement of said first magnetic pattern as the shaft is rotating, said first signal having a frequency indicative of the instantaneous angular velocity of said shaft at said first location;   (d) generating a second signal in a second sensing probe responsive to the movement of said second magnetic pattern as the shaft is rotating, said second signal having a frequency indicative of the instantaneous angular velocity of said shaft at said second location,   (e) determining the phase separation between said first signal and said second signal, said separation being proportional to the torque on said shaft.   
     
     
       15. The method of claim 14 wherein steps (c),(d), and (e) are continuously repeated to provide a continuous indication of torque on the shaft.